Serum PTH is not a good marker for defining a threshold for vitamin D deficiency

• Published in: Endocrine Connections
• Main Authors: Jorde, Rolf, Grimnes, Guri
• Format: Text
• Language: English
• Published: Bioscientifica Ltd 2020
• Subjects: Research; Tromsø
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7274551/; http://www.ncbi.nlm.nih.gov/pubmed/32412426; https://doi.org/10.1530/EC-20-0067

OBJECTIVE: In addition to its skeletal effects, vitamin D may also be important for health in general. It is uncertain what level of serum 25-hydroxyvitamin D (25(OH)D), marker of vitamin D status, is sufficient for these effects. With decreasing serum 25(OH)D levels there is an increase in serum PTH. The point at which this occurs has been considered as a threshold for vitamin D sufficiency. The thresholds found have varied widely and have mainly been based on observational studies. However, to truly establish a threshold for vitamin D effects, this has to be based on randomized controlled trials (RCTs). METHODS: The study included 2803 subjects from a general health survey, the Tromsø study, and pooled individual person data from five vitamin D intervention studies (n = 1544). Serum parathyroid hormone (PTH) and change in PTH after vitamin D supplementation were related to serum 25(OH)D levels in steps of 25 nmol/L (<24, 25–49, 50–74, 75–99, and >99 nmol/L). RESULTS: In the Tromsø study, in the females there was a gradual decrease in serum PTH with increasing serum 25(OH)D with no apparent plateau, whereas in the males the decrease in PTH in subjects with serum 25(OH)D >74 nmol/l was marginal. In pooled RCTs, there was a significant reduction in serum PTH by vitamin D supplementation regardless of baseline serum 25(OH)D level. CONCLUSIONS: The use of the serum PTH–25(OH)D relation from observational studies to determine a threshold for vitamin D sufficiency is highly questionable.